docs: def delete_credential(self, identifier, credential_id=None):
          """Delete the object storage credential.
  
          :param int id: The object storage account identifier.
          :param int credential_id: The credential id to be deleted.
  
          """
          credential = {
              'id': credential_id
          }
  
          return self.client.call('SoftLayer_Network_Storage_Hub_Cleversafe_Account', 'credentialDelete',
                                  credential, id=identifier)